Props are vertical support elements whose height can be adjusted, normally used in construction, comprised of a vertical exterior base tube, known as the lower shaft, which has a support base at its lower end and an interior tube, or upper shaft, that is removable to a lesser or greater extent from the lower shaft to adapt the length of the prop to the distance between the surfaces or elements to be supported by the prop, such as formwork elements.
The props are provided with fastening means that allow the position of the upper shaft to be fixed, once it has been extracted enough from the lower shaft (base tube). These means are normally comprised of a transversal pin that passes through the upper shaft and that at the same time rests on an adjusting nut with handles and attached to the thread that the upper end of the lower shaft has externally.
When the structure that supports the prop on the site has acquired sufficient resistance, the prop is unloaded, i.e. the prop is uncoupled from the formwork element that it supports. To uncouple the prop it is very difficult to manually loosen the adjusting nut in the opposite direction to that of adjustment, since the pressure that the loaded prop is under hinders the turning of said nut with respect to the thread of the lower shaft. It is usual therefore, that the operator hits the nut handles with a hammer or similar, in the direction to loosen it, but this is often the cause of faults in the props. Therefore, to aid the unloading manoeuvre, devices are used for the rapid unloading of props.
Devices are known to aid the unloading of support elements, such as props, based on parts connected to the upper end of said prop, wherein the upper edge has indentations that have a straight step, determining an appreciably horizontal area for the support of a transversal pin that passes through the upper shaft, this state corresponding to the operative or working position of the prop. The parts in question have a recess adjacent to the step, this recess being designed to receive the pin during the descent or fall thereof in the unloading position of the prop. This type of devices for aiding the unloading have the drawback that, due to an accident or a bad manoeuvre, the pin can move towards the edge of the step falling in the recess, which causes the unloading of the prop whilst in working position and the dangers that this involves. Also, to unload the prop, it is necessary to hit the pin strongly so that this falls into the recess, due to the lack of inclination of the surface wherein it is initially supported since if it were more inclined it would increase the risk of the pin accidentally falling in the recess.
Another example of embodiment of a device to aid the unloading of props is disclosed in document ES 2140280, wherein it provides a sliding holder on the prop shaft, that is supported by the adjusting nut and which has two indentations diametrically opposite one other, each one having on one of its sides a sloping step, the bottom of the indentation being rounded, adapted to receive the prop pin. The device is complemented by another part, a sliding cylindrical device on the exterior of the prop shaft, which holds different diametrically opposite extensions, which can fit, for the operative position of the prop, in the holder indentations, preventing the accidental falling of the pin therein. Thus, to aid the unloading of the prop, it is necessary to elevate the cylindrical element, so that the extensions come away from the bottom of the indentations and therefore the pin can slip, due to gravity or being hit, in the sloping step until it penetrates the bottom of the indentations.
In said device to aid the unloading of props, it is necessary to first position the holder, then put the pin through the upper shaft of the prop and keep this supported on the sloping step of the holder, until the complementary part has been positioned on top so that its extensions fit into the bottom of the holder indentations, which complicates the construction of the unit.
The lack of a device for unloading support elements such as props or falsework, that overcomes the drawbacks of the existing devices and that improves the speed and ease of the positioning thereof, is therefore evident.